Both these things started happening after they replaced steering rack at 18k. They also had to replace upper/lower control arms to get rid of creaking sound while turning wheel. Now car vibrates in driver seat and empty passenger seat headreast vibrates tremendously at 78 to 81 mph....which is exactly my speed range for highway driving. Wheels and tires have been indexed and also on car balanced perfectly (throughout entire speed range) to 140mph.

I've done some on-line research:

They (dealer) says laptop system says MAS Mass Airflow Sensor reads ok......I've heard this can be the culprit for idle vibration. Could the MAS read ok and it still be defective?? Also, could it be the ABC system reacting to taut?

On another message board a gentleman in Belguim says hydraulic hose form steering system can send vibrations in park or idle at stop.

While driving, I've heard there has been a problem with parking brake system causing vibrations.

My friends dad had a 600SEL in 1992 and had so many problems between 1992 and 1994 for steering vibrations, he invoked lemon law and got a new one.

He had a vibration, that would come on at 60 mph like clockwork.

Wheels and tires blanced, replaced and all, suspension replaced, steering box and all replaced, mounts, the works, essenstially they replaced the entire suspension, wheels, tires, mounts for the motor and tranny and all steering components and they could not get rid of it.

He had to take the car in many times for this same problem, under warranty, and by 1994 he was so fed up, he walked in and demanded lemon law be invoked and drove out in a brand new 1994 model. 2 years later he switched to BMW 750IL. he drove those for 6 years, then got the new s600 when it came out, the new bodystyle, and he loves it more than the bmws he had.

Now that car was a 1992 and had those problems, first year it was out.

So I doubt it has anything to do with your car, but I would basically take it back, and refuse to leave witht he car in your possesion until the problem is fixed.

If you have to take it back enough times for the same problem, you may be able to invoke lemon law and get a new car.